One of the great challenges in medicine is finding more effective forms of treatment for a large number of life-threatening diseases such as cancer. One of the challenges to be overcome relates to the inadequacies surrounding the ability to administer therapeutic agents so that the therapeutic agents selectively reach the desired targets without damaging healthy cells or being blocked by biological barriers. Thus, to increase efficiency per dose of a therapeutic agent, efforts need to be made in the direction of increasing therapeutic agent delivery, including circumventing the biological barriers that prevent a therapeutic agent from reaching its target.
Of particular interest is the development of drug delivery systems based on nanotechnology that can achieve both targeting (spatial/distribution control) and controlled release (temporal control) of drugs or therapeutic agents. This is because it is believed that if spatial targeting is combined with temporal release, an improved therapeutic index may be obtained. For example, if drug release or activation is made locally at the therapeutic site or biophase, then selectivity will be increased by a multiplication of the spatial selectivity times the advantage of local drug release/activation. Further, the therapeutic index may be improved by a combination of spatially selected delivery and a preferable pattern of release for the therapeutic agent over long time periods or using a pulsatile release, which would be preferable for certain pharmacological activities of the therapeutic agents used in, for example, chronotherapeutics.